One-Pot Synthesis of a Linear [4]Catenate Using Orthogonal Metal Templation and Ring-Closing Metathesis

Abstract

The efficient synthesis of well-defined, linear oligocatenanes possessing multiple mechanical bonds remains a formidable challenge in the field of mechanically interlocked molecules. Here, a one-pot synthetic strategy is described to prepare a linear [4]catenate using orthogonal metal templation between a macrocycle precursor, composed of terpyridine and phenanthroline ligands spaced by flexible glycol linkers, and a closed phenanthroline-based molecular ring. Implementation of two simultaneous ring-closing metathesis reactions after metal complexation resulted in the formation of three mechanical bonds. The linear [4]catenate product was isolated in 55% yield as a mixture of topological diastereomers. The intermediate metal complexes and corresponding interlocked products (with and without metals) were characterized by nuclear magnetic resonance, mass spectrometry, gel permeation chromatography, and UV−vis absorption spectroscopy. We envision that this general synthetic strategy may pave the way for the synthesis of higher order linear oligocatenates/catenanes with precise molecular weights and four or more interlocking molecular rings.

Distinctive features and challenges in catenane chemistry

“…50,51 A few other linear [4]-and [5] catenanes from either stepwise or one-pot synthesis have also been recently reported. [52][53][54][55] In 2017, Rowan and co-workers have explored the use of a metallopolymer to obtain [n]catenanes. 56 The metallopolymer consists of ditopic macrocycles and linear components coordinated via Zn 2+ ions in an alternate fashion, from which a mixture of branched, linear and cyclic [n]catenanes were obtained upon ring-closing metathesis (Fig.…”

Metalation/Demetalation as a Postgelation Strategy To Tune the Mechanical Properties of Catenane-Crosslinked Gels

“…This difference in mass is attributed to isomerization of the terminal alkene during ring-closing metathesis (RCM), resulting in loss of a methylene unit. This has been observed previously in RCM and is commonplace in the synthesis of small and oligocatenanes. , After complete characterization, 14 was incorporated into organogels to evaluate the extent to which control over the crosslinker’s conformational motions impacted the gel’s mechanical properties.…”

“…This has been observed previously in RCM 28 and is commonplace in the synthesis of small and oligocatenanes. 29,30 After complete characterization, 14 was incorporated into organogels to evaluate the extent to which control over the crosslinker's conformational motions impacted the gel's mechanical properties.…”

An “All-in-One” Synthetic Strategy for Linear Metalla[4]Catenanes

“…). , One fascinating and challenging synthetic target in this field is the family of linear [ n ]­catenanes that possess four or more rings (Figure ). , Effective methods for the synthesis of linear [ n ]­catenanes ( n ≥ 4) remain rare, especially quantitative syntheses and those with a definitive structural characterization. − The majority of linear [ n ]­catenanes ( n ≥ 4) have relied on template-directed synthesis by tetracationic cyclophane π-acceptors ( A ) and crown-ether-based π-donors ( D ), for example, the linear [5]­catenanes from the group of Stoddart, also known as “Olympiadanes” owing to their topological similarity to the logo of the Olympic games. − However, their intrinsic limitations, tedious synthesis, and unsatisfactory yields have limited the development of linear [ n ]­catenanes ( n ≥ 4) …”